Streptococcus pneumoniae is normally found as an inhabitant of the human nasopharynx that becomes pathogenic in response to environmental changes. As a pathogen, it spreads to the lungs (pneumonia), the central nervous system (meningitis), and the middle ear (otitis media). Mortality and morbidity due to S. pneumoniae is seen primarily in the very young and elderly. Signal transduction plays a major role in sensing the environment of S. pneumoniae and in its decision to become pathogenic. Our long-term goal is to study global gene regulation by signal transduction, particularly to learn about the intracellular events that occur following activation of signal transduction pathways. The proposed studies will focus on the response regulator RitR, on a Serine/Threonine kinase phosphatase pair, and on their mutual interactions. Pneumococci that lack RitR are unable to infect the lung, which makes this protein an attractive target to study in connection with the development of antimicrobial chemotherapy. Serine/Threonine kinases and phosphatases are also necessary for virulence in S. pneumoniae. It is our working hypothesis that: (1) RitR lacks a cognate His kinase, but interacts with a Ser/Thr kinase phosphatase system;(2) RitR is a global regulatory protein in S. pneumoniae which represses the synthesis of the Piu heme transporter, and (3) Ser/Thr kinase and phosphatase are required for Piu heme transporter expression. The specific aims of this proposal are: (1) To characterize the novel interaction between RitR, a Ser/Thr Kinase, and Ser/Thr phosphatase present in S. pneumoniae, (2) To examine how these proteins regulate expression of the Piu heme transporter, and (3) To identify other genes regulated by the RitR/Stp/Stk complex. PUBLIC HEALTH RELEVANCE: Streptococcus pneumoniae is normally found as an inhabitant of the human nasopharynx that becomes pathogenic in response to environmental changes. As a pathogen, it spreads to the lungs (pneumonia), the central nervous system (meningitis), and the middle ear (otitis media). Mortality and morbidity due to S. pneumoniae is seen primarily in the very young and elderly. Signal transduction plays a major role in sensing the environment of S. pneumoniae and in its decision to become pathogenic. Our long-term goal is to study global gene regulation by signal transduction, particularly to learn about the intracellular events that occur following activation of signal transduction pathways. The proposed studies will focus on the response regulator RitR, on a Serine/Threonine kinase phosphatase pair, and on their mutual interactions. Pneumococci that lack RitR are unable to infect the lung, which makes this protein an attractive target to study in connection with the development of antimicrobial chemotherapy. Serine/Threonine kinases and phosphatases are also necessary for virulence in S. pneumoniae. It is our working hypothesis that: (1) RitR lacks a cognate His kinase, but interacts with a Ser/Thr kinase phosphatase system;(2) RitR is a global regulatory protein in S. pneumoniae which represses the synthesis of the Piu heme transporter, and (3) Ser/Thr kinase and phosphatase are required for Piu heme transporter expression. The specific aims of this proposal are: (1) To characterize the novel interaction between RitR, a Ser/Thr Kinase, and Ser/Thr phosphatase present in S. pneumoniae, (2) To examine how these proteins regulate expression of the Piu heme transporter, and (3) To identify other genes regulated by the RitR/Stp/Stk complex.